Rocker arm for valve control apparatus

ABSTRACT

To provide a rocker arm for a valve control apparatus of an automobile engine, which enables downsizing of the valve control apparatus and provides improved fuel economy of the engine. The rocker arm is provided with: a top plate; at least one upright wall section; a cam slide section, formed on top of the top plate, in contact with a cam mounted on a camshaft; a supporting member for rockably supporting the rocker arm about the rocking center of the supporting member; and a pad face, formed at the other end of the rocker arm, in contact with a valve system. Said at least one upright wall section has a smaller width than the top plate, and extends from the top plate at a substantially right angle.

FIELD OF THE INVENTION

This invention relates to a rocker arm for use with a valve controlapparatus for controlling the valve open/close operation of anautomobile engine via a rocker arm rocked by the cam of a camshaft, therocker arm providing an improved the fuel economy of the engine andenabling down sizing of the valve control apparatus

BACKGROUND ART OF THE INVENTION

A rocker arm rocked by a cam driven by a camshaft of the engine forlifting and lowering an engine valve is disclosed in a patent documentlisted below. The rocker lever (rocker arm) 1 of Patent Document 1 has asemi-spherical recess 2 engaged with the semi-spherical end 4 of asupport member 3 for rockably supporting the rocker lever 1 in contactwith the base section (or valve stem) of a gas exchange valve (enginevalve) urged by a valve spring for closing the valve (not shown).Provided at the center of the rocker lever (rocker arm) 1 is a roller 6in contact with a camshaft (not shown). The rocker lever 1 opens theengine valve by pushing down the roller 6 (not shown) and allows theengine valve to be closed by means of a valve spring (not shown) urgingthe valve.

PRIOR ART DOCUMENT

PATENT DOCUMENT: JPA Laid Open H10-37719

SUMMARY OF THE INVENTION Objects to be Achieved by the Invention

In general a camshaft is subjected to a force of a valve spring urgingthe valve stem to close the valve and a frictional torque generatedbetween the rocker arm and the cam pushing down the rocker arm inopposition to the force of the valve spring during a valve openingperiod. This frictional torque impedes the rotation of the camshaft.Since this frictional torque lowers the fuel economy of the engine, thevalve control apparatus of Patent Document 1 utilizes a rocker lever 1having a roller 6 in contact with the cam so as to reduce the frictionbetween the cam and the rocker arm, and hence the frictional torqueacting on the camshaft.

However, although the roller 6 can reduce the friction between the camand rocker lever 1, such roller 6 greatly increase the weight of therocker lever 1, since the roller 6 requires needle bearings for example.An increase in weight of the rocker lever 1 entails an increase in theinertial moment of the rocker lever 1, which implies that a strongervalve spring is required to close the valve. However, a stronger valvespring will cause the roller 6 to exert a stronger force on the cam,thereby increasing the frictional torque acting on the camshaft.

As a consequence, in spite the roller 6 can reduce the frictionaltorque, the rocker lever 1 having such roller 6 suffers from anincrement of the frictional torque due to the increased spring force ofthe valve spring. Hence, reduction of the frictional torque by the useof cam in rolling contact with the roller 6 is overwhelmed by anincrement of the frictional torque due to an increment of the valveforce of the valve spring. This is a serious problem from the point ofthe fuel economy of the engine. The use of a roller poses a furtherproblem that it increases the dimensions of the rocker lever 1, makingit difficult to downsize the valve control apparatus.

In view of the problems mentioned above, the present invention isdirected to an improved rocker arm operably coupled to the camshaft,which enables not only reduction of the disadvantageous frictionaltorque that impedes the rotation of the camshaft but also enablesdownsizing of the valve control apparatus, thereby facilitatingimprovement of the fuel economy of the engine.

Means for Achieving the Objects

An inventive rocker arm for a valve control apparatus in accordance withclaim 1 has a top plate and at least one upright wall section, wherein

-   -   the top plate is:        -   provided on top thereof with a cam slide section in contact            with a cam of a camshaft;        -   supported at one end thereof by a supporting member rockably            about the rocking center of the supporting member; and        -   is provided at the other end thereof a pad face in contact            with a valve system, and    -   said at least one upright wall section has a smaller width than        the top plate, and extends from the top plate at a substantially        right angle.

In the rocker arm of claim 1, in order to reinforce the top platesubjected to the reactive force of the valve spring acting on the padface and the cam force acting on the cam slide section, said at leastone upright wall section is integrated with the top plate.

(Function) In the rocker arm of the valve control apparatus of claim 1,the top plate has a minimum possible thickness, yet it is reinforced bythe upright wall having a thickness less than that of the top plate, sothat the weight and inertial moment of the rocker arm are significantlyreduced. As a consequence, the valve control apparatus equipped with therocker arm of claim 1 can use an extremely light-weight valve spring,which in turn permits great reduction of the frictional torque arisingfrom the force of the valve spring and applied to the camshaft. That is,a torque that would otherwise impede the rotation of the camshaft isgreatly reduced.

As a result, in the rocker arm of claim 1, reduction of the frictionaltorque due to the elimination of a roller and reduction of the weight(or the urging force) of the valve spring outweighs generation of aminor frictional torque that takes place between the rocker arm and thecam sliding on the rocker arm.

In the rocker arm of the valve control apparatus of claim 1, at leastone of the cam slide section and pad face of the rocker arm may besurface treated to reduce its frictional coefficient, as recited inclaim 2.

(Function) In the rocker arm of claim 2, the frictional coefficient ofthe surface treated section is reduced, thereby reducing the frictiongenerated between the cam and the cam slide section or between the valvestem and pad face, which in turn further reduces the frictional torqueacting on the camshaft.

In the rocker arm for a valve control apparatus of claim 1 or 2, the topplate may have at least one hole in a region except for the cam slidesection, as recited in claim 3.

(Function) In the rocker arm of claim 3, the weight of the rocker arm isfurther reduced by the formation of the hole. As a consequence the forceof the valve spring transmitted to the cam, and hence the frictionaltorque applied to the camshaft, is further reduced.

In the rocker arm a valve control apparatus in accordance with any oneof claims 1 through 3 may have at least one hole formed in the uprightwall section, as recited in claim 4.

(Function) In the rocker arm of claim 4, the weight of the rocker arm isreduced still further that the frictional torque applied to the camshaftis reduced still further.

In the rocker arm for a valve control apparatus in accordance with claim4, the hole formed in the upright wall section may be formed on therocking trajectory of the cam slide section rocking about its rockingcenter, as recited in claim 5.

(Function) In the rocker arm of claim 5, the hole thus formed on therocking trajectory of the cam slide section reduces the weight of thatportion of the rocker arm in contact with the cam. Accordingly, theinertial moment of the cam pushing the rocker arm of claim 5 is reduced.

In the rocker arm for a valve control apparatus in accordance with anyone of claims 1 through 5, the cam slide section may be provided withoil grooves, as recited in claim 6.

(Function) In the rocker arm of claim 6, oil fed to the cam slidesection in contact with the cam stays in the oil grooves and forms anoil film between the cam and cam slide section. As a result, thefriction between the cam and cam slide section is reduced, whichimproves the wear resistances of the cam and cam sliding section.

In the rocker arm for use with a valve control apparatus in accordancewith any one of claims 1 through 6, at least one of the cam slidesection and the pad face can be configured to have a convex transversecross section, as recited in claim 7.

If both of the cam slide section and pad face have flat transverse crosssections, the pad face is likely to be inclined relative to the valvespring in the event that the cam slide section is inclined relative tothe cam due to a backlash of the rocker arm. In this case, a corner ofthe cam slide section may come into contact with the cam and cause anunexpected frictional force, while the pad face may come into contactwith a corner of the valve stem and cause an unexpected frictionalforce. Such frictional forces will impede the rotation of the camshaft.

(Function) If, on the other hand, at least one of the cam slide sectionand pad face has a convex transverse cross section, the corner of eitherthe cam slide section or the valve stem is less likely to come intocontact with the cam or pad face. As a consequence no corner-planecontact is less likely to take place between the cam and cam slidesection or between the pad face and the valve stem. Thus, in the rockerarm of claim 7, the cam can push down the cam slide section of therocker arm downward with a reduced inertial moment, thereby facilitatingthe stability of open/close operations of the engine valve.

The rocker arm for use with a valve control apparatus in accordance withany one of claims 1 through 7, wherein the upright wall section has apair of inner walls each spaced apart from the periphery of the valvestem by a distance in the range from 0.1 mm to 1 mm.

(Function) Since in this case there is provided an adequate allowancebetween the valve stem and the upright walls, disadvantageous frictionwill not take place between them, thereby facilitating the stability ofthe open/close operations of the engine valve.

RESULTS OF THE INVENTION

The rocker arm of claim 1 has a greatly reduced weight and hence givesrise to much less frictional torques, and hence it has greatly improvedthe fuel economy of an engine as compared with conventional rocker arms.Further, since the rocker arm has no rollers, it can be downsized withless components. It is not troubled with abnormal wear of needlebearings and/or shaft.

In the rocker arm according to any one of claims 2 through 4 africtional torque acting on the camshaft is further reduced, therebyimproving the fuel economy of the engine.

In the rocker arm of claim 5, the cam can push down the cam slidesection of the rocker arm with a reduced torque, thereby reducing thefrictional torque acting on the camshaft still further and improving thefuel economy of the engine still further.

In the rocker arm of claim 6, the frictional force that takes placebetween the cam and cam slide section is reduced, thereby furtherreducing the frictional torque acting on the camshaft and improving thefuel economy of the engine still further.

In the rocker arm of claim 7, at least one of the frictional force thattakes place between the cam and cam slide section and the frictionalforce that takes place between the pad face and the valve stem isreduced, thereby reducing the frictional torque acting on the camshaftstill further and hence improving the fuel economy of the engine.

With the rocker arm of claim 8, stability of the valve movement isfacilitated by the fact that the friction between the valve and theupright walls is reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1( a) is a schematic perspective view of a rocker arm for a valvecontrol apparatus and FIG. 1( b) is its plan view in accordance with afirst embodiment of the invention.

FIG. 2( a) is a cross section of the rocker arm taken along line A-A ofFIG. 1( b); FIG. 2( b) a bottom view of the rocker arm; and FIG. 2( c) atransverse cross section of the cam slide section taken along line B-Bof FIG. 2( a).

FIG. 2A(a) is a cross section of a modified cam slide section whosetransverse cross section is convex as shown in FIG. 2( c). FIG. 2A(b)shows modified pad face and valve stem having convex cross sectionstaken along line E-E of FIG. 2( a).

FIG. 3 is a schematic diagram illustrating movement of a valve controlapparatus equipped with the rocker arm in accordance with a firstembodiment of the invention.

FIG. 4( a) is a perspective view of a rocker arm in accordance with asecond embodiment of the invention; and FIG. 4( b) is plan view of thesecond rocker arm.

FIG. 5( a) is a cross section of the second rocker arm of FIG. 4( b)taken along line C-C of FIG. 4( b); FIG. 5( b) is a bottom view of thesecond rocker arm; and FIG. 5( c) is a cross section taken along lineD-D of FIG. 5( a).

FIG. 6 is a perspective view of a rocker arm in accordance with a thirdembodiment of the invention.

BEST MODE FOR CARRYING OUT THE INVENTION

The invention will now be described in detail by way of example withreference to a first embodiment shown in FIGS. 1 through 3. In whatfollows the upper, lower, right, and left portion of a rocker arm shownin the respective figures will be denoted by symbols Up, Lw, Le, and Ri,respectively, and transverse (front-rear) direction by Fr-Re.

A rocker arm 10 of a valve control apparatus of the first embodiment hasa metal top panel 11 and a pair of upright wall section 12. The toppanel 11 consists of a protrusion 13 projecting upward, a semi-sphericalengaging section 14 of the supporting member 16 contiguous to the leftend of the protrusion 13, and a section 15, contiguous to the right endof the protrusion 13, supported by the valve stem 17 a of an enginevalve 17. (The section 15 will be hereinafter referred to as valve stemsupport section 15)

The protrusion 13 includes a cam slide section 18 (shaded area in FIG.1( a) and FIG. 3) on which the cam of the camshaft (not shown) slides,and a planar section 19 that extends between lines L1 and L2 in FIG. 3.The cam slide section 18 has an arcuate or convex surface projectingupward, while the planar section 19 extends downward from the left endof the cam slide section 18. The engaging section 14 of the supportingmember 16 is contiguous to the left end of the planar section 19 and hasa substantially semispherical shape that protrudes upward. Formed insidethe semi-spherical engaging section 14 is a semi-spherical engaging face20 for engagement with the semi-spherical top end of the supportingmember 16.

On the other hand, the supporting section 15 has an arcuate section,contiguous to the right end of the cam slide section 18 and protrudingdownward. Formed below the supporting section 15 is a pad face 22 whichabuts against the valve stem 17 a. In order to reduce the frictioncoefficient, or enhance wear resistance and/or hardness, of at least oneof the cam slide section 18 and the pad face 22, its surface ispreferably surface treated with DLC coating for example. This surfacetreatment reduces friction between the cam (not shown) and the cam slidesection 18, or friction between the pad face 22 and valve stem 17 a,which in turn reduces a frictional torque that acts on the camshaft toimpede its rotation, thereby improving the fuel economy of the engine.

Although the cam slide section 18 can be a simple flat surface, it ispreferably provided with a multiplicity of oil grooves 25 as shown inFIG. 1. In the first embodiment, the rocker arm is provided with amultiplicity of longitudinal linear parallel oil grooves 25. When alubricant oil is supplied to the oil grooves 25, an oil film is formedbetween the cam and cam slide section 18, which increases their wearresistance.

A pair of straight upright wall section 12 extend downward from thefront and rear ends of the protrusion 13 and supporting section 15. Thepaired straight walls 12 are formed such that the total transversethickness W2 of the upright walls is smaller than the transverse widthW1 of the top panel 11. The rocker arm 10 has a generally invertedU-shape transverse cross section, so that it has a reduced weightbecause of a hollow section 24 under the U-shape section. Each of thepaired upright wall section 12 is provided with a transversethrough-hole 23. The through-holes 23 may be formed in a region of thetop panel 11 excluding the planar section 19, cam slide section 18, andpad face 22. Thus, the rocker arm 10 is reduced in weight by thethrough-holes 23. Such trimming of weight of the rocker arm 10 helpsreduce the friction between the cam and cam slide section 18, which inturn reduces the frictional torque that acts on the camshaft to impedethe rotation of the camshaft, thereby improving the fuel economy of theengine.

FIG. 2A shows a modification of the cam slide section and pad face ofthe first embodiment. A rocker arm 10′ shown in FIG. 2A has the samestructure as the rocker arm 10 except for a cam slide section 18′ and apad face 22′. The cam slide section 18′ of FIG. 2A(a) has a convextransverse cross section, protruding upward towards the cam 9. The padface 22′ of the supporting section 15′ of FIG. 2A(b) has a convextransverse cross section protruding towards the upper end 17 e′ of thevalve stem 17 a′ of an engine valve 17′.

Because of backlashes of the cam 9, cam slide section 18′, pad face 22′,and valve stem 17 a′, it may happen that they incline in the transversedirection with respect to a vertical line L5 passing through the rockerarm. Should either one of the opposite corners 18 a′ and 18 b′ of thecam slide section 18′ touch the slide face 9 a of the cam 9, or of theopposite corners 17 b′ and 17 c′ of the upper end 17 e′ of the valvestem 17 a′ touch the pad face 22′, frictional dragging forces would takeplace on the contact faces, which impedes smooth open/close operation ofthe engine valve.

In the example shown in FIG. 2A, the cam slide section 18′ and pad face22′ are convexed in the transverse direction so that the corners 18 a′and 18 b′ of the rocker arm 10′ are less likely to touch the slide face9 a of the cam 9, and so are the corners 17 b′ and 17 c′ to touch thepad face 22′. Accordingly, the rocker arm 10′ of FIG. 2A has anadvantage that it is free of friction that would otherwise take placebetween the cam slide section 18′ and pad face 22′ and impede therotation of the camshaft.

It is noted that the slide face 9 a of the cam 9 and the upper section17 e′ of the valve stem 17 a′ are also convex in the transversedirection as shown in FIG. 2A. In this case, the corners 9 b and 9 c ofthe cam 9 and the corners 18 a′ and 18 b′ of the cam slide section 18′will be less likely to touch the cam slide section 18′ and slide face 9a, respectively, and so will be the corners 17 b′ and 17 c′ of the upperend 17 e′ of the valve stem 17 a′ to touch the pad face 22′.

Incidentally, it is preferable to provide spaces C1 and C2, orallowances, between the paired inner walls 12 a′ and 12 b′ of theupright wall section 12′ of the rocker arm 10′ and the periphery 17 d′of a valve stem 17′ as shown in FIG. 2A(b). This is also the case withother embodiments. It is preferred that the spaces C1 and C2 have atotal width (C1+C2) in the range from 0.1 mm to 1 mm. With the rockerarm 10′ having such appropriate spaces C1 and C2, open/close operationof the valve is stabilized.

With the engaging section 20 in engagement with the semi-spherical head21, the rocker arm 10 is rockably supported by the supporting member 16about a rocking center L0 of the semi-spherical head 21 as shown in FIG.3. It is noted that in FIG. 3 only the rocker arm 10 is shown in crosssection and that the top panel 11 is shown not hatched. The valve stem17 a of the valve, urged upward by a valve spring (not shown) forclosing the valve, forces the pad face 22 upward. As the pad face 22 isforced upward, it pushes the cam of the camshaft (not shown) locatedabove the pad face 22. Thus, the cam is always in sliding contact withthe cam slide section 18 while the camshaft is in rotation. The rockerarm 10 opens the engine valve 17 when pressed downward D1 as shown inFIG. 3 by the rotating cam, and closes the valve when pushed upward D2as shown in FIG. 3 by the valve spring which overrides the cam force ofthe rotating cam.

Thus, the cam slide section 18 (between line L1 and L2 of FIG. 3) rocksabout the rocking center L0. The holes 23 of the upright wall section 12are preferably formed in the region between dotted lines L3 and L4 wherethe dotted lines L3 and L4 are the trajectories of the rocking lines L1and L2, respectively. In this case, the portions of the upright wallsection 12 subjected to the cam force are reduced in weight. Then, thetorque required for the cam to push down the rocker arm 10 is reduced,which in turn reduces the frictional torque that impedes the rotation ofthe camshaft, thereby improving the fuel economy of the engine.

Referring to FIGS. 4 and 5, there is shown a rocker arm 29 of a valvecontrol apparatus in accordance with a second embodiment of theinvention. The rocker arm 29 are the same in structure as the rocker arm10 of the first embodiment except that the upright wall section 31 isdifferent in shape from the upright wall section 12 of the firstembodiment and that the upright wall section 31 has a stiffening rib 32.

In addition to the upright wall section 31, the rocker arm 29 has ametallic top section 30. The top panel 30 is structurally the same asthe top panel 11 of the first embodiment, and comprises a protrudingportion 33, an engaging section 34 of a supporting member (not shown),and a section 35 supported by a valve stem (referred to as valve stemsupport section 35) of the valve stem (with reference numerals 13, 14,and 15 are renumbered as 33, 34, and 35, respectively, for the top panel30). The protruding portion 33 has a cam slide section 36 and a planarsection 37. The engaging section 34 is a substantial semi-sphereprotruding upward, and contiguous to the left end of the planar section37. Formed inside the engaging section 34 is a substantiallysemi-spherical engagement face 38 for engagement with the semi-sphericalhead of the supporting member (not shown). The valve stem support 35 isprovided on the lower surface thereof with a pad face 39 for abutmentwith the valve stem (not shown) which is urged upward by a valve spring.To minimize friction between the cam slide section 36 and the pad face39, at least one of the cam slide section 36 and the pad face 39 ispreferably subjected to DLC coating, for example, for surface-treatment,as in the first embodiment. Also, as in the first embodiment, the camslide section 36 is preferably provided with a multiplicity of oilgrooves 42 to secure a lubricant film on the cam slide section 36.

In addition, a pair of upwardly projecting ribs 32 are formed on the toppanel 30 integrally with the planar section 37 and engaging section 34.The ribs 32 reinforces the rocker arm 29 via the top panel 30, and addsmore stiffness thereto, thereby improving the responsiveness of thevalve control apparatus. These ribs 32 may be also provided between theplanar section 19 and the semi-spherical engaging section 14 of thefirst embodiment.

The upright wall section 31 depends from the lower surface of the toppanel 30. The upright wall section 31 shown in FIG. 5( b) consists of anupright wall 40 extending downward from the transverse center of theprotruding portion 33, a pair of downward upright walls 41 extendingbetween the rear and front ends of the valve stem support 35, and aU-shape section 43. The upright wall 40 is integral with the pairedupright walls 41 and the U-shape section 43. The total sum of thetransverse width W3 (front-to-rear width) of the wall 40 and the widthsof the paired upright walls 41 (two times W4) is smaller than the widthW1 of the top panel 30. The rocker arm 29 has a substantially T-shapetransverse cross section as shown FIG. 5( c) at a position where thewall 40 is formed, and has an inverted U-shape cross section as shown inFIG. 2( c) at a position where the paired upright walls 41 are formed.

The upright wall 40 has a transverse through-hole 44. The transversethrough-hole 44 can be formed anywhere in the rocker arm 29 except forthe cam slide section 36 and pad face 39. The rocker arm 29 is reducedin weight by the transverse through-hole 44. To effectively reduce theweight of the portion of the rocker arm pushed by the cam, thetransverse through-hole 44 is preferably formed within the upright wallsection 31 on the trajectory of the cam slide section 36, as are formedthe holes 23 in the upright walls 23 of the first embodiment

FIG. 6 shows a rocker arm 50 in accordance with a third embodiment ofthe invention. The rocker arm 50 has essentially the same structure asthe rocker arm 10 of the first embodiment except that the rocker arm 50has oil grooves 51 different in shape from the oil grooves 25 shown inFIG. 1. The rocker arm 50 is provided on the cam slide section 18′ witha multiplicity of oil grooves 51 in the form of dimples. Such multipleoil grooves 51 can also retain much oil to form a strong oil filmbetween the cam (not shown) and the cam slide section 18′, therebyfurther improving the wear resistance of the elements involved.

REFERENCE NUMERALS AND SYMBOLS

9 cam of camshaft

10 rocker arm

11 top panel

12 and 12′ upright walls

12 a′ and 12 b′ inner wall surface

16 supportive member (for pivot type lash adjuster)

17 a and 17 a′ valve stem of engine valve

17 d′ periphery of valve stem

18, 18′, and 18″ cam slide sections

22 and 22′ pad faces

23 holes

25 oil grooves

29 rocker arm of valve control apparatus

30 top panel

31 upright walls

36 cam slide section

39 pad face

42 oil grooves

44 through-hole

50 rocker arm of valve control apparatus

51 oil grooves

L0 rocking center

1. A rocker arm for a valve control apparatus comprising a top plate andat least one upright wall section, characterized in that: said top plateis: provided on top thereof with a cam slide section in contact with acam of a camshaft; supported at one end thereof by a supporting memberrockably about the rocking center of the supporting member; and isprovided at the other end thereof with a pad face in contact with avalve system, and said at least one upright wall section has a smallerwidth than the top plate, and extends from the top plate at asubstantially right angle.
 2. The rocker arm according to claim 1,wherein said at least one of the cam slide section and pad face of therocker arm has a surface-treated face having a reduced frictionalcoefficient.
 3. The rocker arm according to claim 1, wherein the topplate has at least one hole formed in a region except for the cam slidesection of the top plate.
 4. The rocker arm according to claim 1,comprising at least one hole in the upright wall section.
 5. The rockerarm according to claim 4, wherein the hole formed in the upright wallsection is formed on the rocking trajectory of the cam slide sectionrocking about the rocking center.
 6. The rocker arm according to claim1, wherein the cam slide section has oil grooves.
 7. The rocker armaccording to claim 1, wherein at least one of the cam slide section andthe pad face has a convex transverse cross section.
 8. The rocker armaccording to claim 1, wherein the upright wall section has a pair ofinner walls each spaced apart from the periphery of the valve stem by adistance in the range from 0.1 mm to 1 mm.